A sex offender is a person who is convicted of a sexual offense. Sexual
offenses includes such crimes as rape, sodomy, and sexual abouse. Most
states have laws, which vary by state, on registration of sexual offenders. A registered sex offender is defined as a person who exhibits characteristics showing a tendency to victimize or injure others and has been convicted of a sex crime listed in the relevant state statutes, has been convicted of attempting to commit one of those crimes, or has been found guilty except for insanity of one of those crimes.
The registered sex offenders are required to notify the local community
authorities of their residence so that the public may have access to information
about sexual predators in their neighborhood.

Rape is generally defined as sexual intercourse with a person by forcible
compulsion; or sexual intercourse with a person who is incapable of consent
by reason of being physically helpless or mentally incapacitated; or sexual
intercourse with an underage person. Sodomy is defined similarly to rape,
except that it involves deviate sexual conduct, as opposed to intercourse.
Sexual abuse involves similar elements of force or lack of consent, but
involves sexual contact, rather than intercourse or deviate sexual acts.

A sexual predator is defined as a person who is an adult or juvenile who has been convicted of, or pleaded guilty to, committing a sexually oriented offense and who is likely in the future to commit additional sexually oriented offenses. Definitions vary by state, so local laws need to be consulted to determine
the applicabe law in your area.